An organic electroluminescent display has advantages of self-luminescence, fast response, wide viewing-angle, high brightness, bright color, low thickness, light weight and the like, thus, an organic electroluminescent display technology has been one of the development trends in the flat-panel display field.
Currently, an organic electroluminescent layer in the organic electroluminescent display is formed mainly by using the following two methods, wherein a first method makes use of an evaporation process, and the first method is suitable to small organic molecules and has features that the organic electroluminescent layer can be formed without a solvent, a thickness of a film is uniform, while the equipment investment is high, the material utilization is low and then the method is not suitable for production of a large-sized product; a second method: performing a process such as spin coating, ink-jet printing, nozzle coating and screen printing using a solution of organic electroluminescent material, and such methods are suitable for polymer material and small soluble molecules, and have a feature of being low equipment cost, and the methods have prominent advantages in large-scale and large-sized production. In particular, the ink-jet printing can accurately spray a solution to a pixel region, and as this method has the high material utilization and can achieve the large-sized production, it is deemed an important manner for achieving mass production of a large-sized organic electroluminescent display.
The ink-jet printing process needs to form a pixel defining layer (PDL) on a substrate in advance to define pixel regions into which ink droplets are accurately spray. Usually, a cross-section shape of the PDL is mainly a trapezoid, as shown in FIG. 1, a pixel defining layer 20 is formed on the substrate 10, an organic light emitting layer 30 is formed in a pixel region 40 defined by the pixel defining layer 20, herein a material for forming the pixel defining layer 20 is lyophobic material, thus it can be guaranteed that the ink droplets do not flow over the pixel region when the organic light emitting layer 30 is ink-jet printed. However, due to a large surface energy difference at a contact between the ink droplets and the pixel defining layer 20, a large slope angle of the PDL and a self-desiccation of the ink droplets, it is easy to form a non-uniform film with a smaller thickness at a edge and a larger thickness in the middle after drying the ink droplets, in particular, the thickness of the film is very small at an edge of the pixel region, just as shown by a region A circled by a dotted circle in FIG. 1. Therefore, a resultant structure may render a pinhole at the edge of the pixel region and thus render the electric leakage. Moreover, for the pixel defining layer shown in FIG. 1, an area of a region B of the light emitting layer 30 for emitting light is substantially equal to that of the whole pixel region 40, and because the thickness of the light emitting layer in the light emitting region B is not uniform, the brightness in the pixel region is not uniform.